In control units, particularly in a motor vehicle, an existing memory, particularly a read-only memory is replaced or faded out in order thereby to be able to adjust values or make settings while the control unit is in operation. Besides motor vehicle control units, other control units are also conceivable in this context, such as aviation units or even machine tools and machining centers, control units of automation technology, etc.
Such an emulation device for a control unit is described in German Published Patent Application No. 39 17 979, a data manipulating device being provided and an external and, particularly, a serial interface of the operator unit of the control unit for changing data of a read-write memory that is contained in the control unit. A switching device is provided for switching the read access in the data manipulation device, which switches over, on the one hand, between the read-write memory, and on the other hand a data program read memory.
In the same vein, German Published Patent Application No. 41 07 052 describes a device for the application of control units in which, likewise, the data/program read memory of the control unit is replaced by a data manipulation device having a read-write memory, to which likewise an operator unit is connected via a serial interface. Here too, a switching device is provided in which the read-write memory is connected in a first cycle to the control unit for reading out data, and in a second cycle to the serial interface for reading in or reading out data.
The switching over between the memories is performed by the connected application unit, in this instance. In some microcontrollers, the overlaying memory is made up of several regions, in this context, which are able to be activated only region by region. In the process, it is frequently not preventable that the control unit program accesses inconsistent data during the switching over between the regions. This is conditioned upon the fact that, because of the successive switching in of the regions, an intermediate reading comes about, with regard to the overlaid storage area, during the switching over process which does not correspond to the desired final state of the data. Thus, the control unit program accesses data which in part are made up of various storage areas and various regions. Because of this overlapping, what may happen is that the control unit software makes calculations using wrong data, which may lead to a corrupted result, and in the worst case even to a program crash.
Thus, conventional arrangements have not been able to yield optimum results in all regards.